1. Field of the Invention
The present invention relates to an active ray curable ink jet solventless ink, an image forming method using the same, and an ink jet recording apparatus.
2. Description of the Related Art
In recent years, ink jet recording system has been widely applied in various printing fields including photograph, miscellaneous printings, marking, special printing for color filer or the like, by virtue of its simplicity and inexpensiveness in image formation. In particular, it has also been made possible to obtain image quality equivalent to that of silver salt photograph by using recording apparatuses capable of ejecting and controlling fine ink dots, or using inks having an improved color reproducibility, durability and ejection suitability in combination with specialized paper having a largely improved ink absorption property, color developing property for colorant materials and surface glossiness. That is, the improved image quality of the recent ink jet recording system cannot be accomplished without a perfect combination of the recording apparatus, ink and specialized paper.
The ink jet system always in need of the specialized paper, however, limits the range of available recording media, and undesirably increases cost for the recording media. Much effort has thus been made on recording by the ink jet system onto media to be printed which differs from the specialized paper. Specific examples of the ink jet system include phase-transfer ink jet system using a solid wax ink at room temperature, solvent ink jet system using an ink mainly composed of a quick-drying solvent, and active ray curable ink jet system allowing the ink to crosslink by UV or electron beam irradiation after recording an image.
Among others, the UV ink jet system has recently attracted public attention because of its various advantages over the solvent ink jet system in that it is causative of only a relatively low odor, has a quick-drying property, and allows recording on media having no ink absorption property. For example, Japanese Laid-Open Patent Publication No. 6-200204, and Published Japanese Translation of PCT International Publication for Patent Application No. 2000-504778 disclose ultraviolet ray curable ink jet inks.
It is, however, impossible to form high-definition images on various recording material even with these inks, because ink dot diameter after the placement tends to largely vary depending on types of the recording material or working environment.
Specific examples of the ultraviolet ray curable ink ever proposed include radical-polymerizable ultraviolet ray curable inks using photo-polymerizable compounds mainly composed of acryl-base compositions (see European Patent No. 540,203, Brochure of International Publication No. 97/31,071 and Brochure of International Publication No. 99/29,788, for example), but the following problems remain unsolved.
The radical-polymerizable ultraviolet ray curable ink is labile to oxygen inhibition in an oxygen-participated environment because of its polymerization mechanism, and tends to degrade the curing property so as to degrade the image quality. The large curing shrinkage thereof is also causative of wrinkle formation or curling of the recording material.
The radical-polymerizable compounds are also disadvantageous in that they generally have a large viscosity, and thus make it difficult to form high-definition images by the ink jet recording due to their insufficient ejection stability.